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#include <cstdio>
#include <vector>
#include <utility>

using namespace std;

const int N = 8005;

char s[N];
int acc[2][N];

int main() { 
    int n, k, t;
    scanf("%d%d%d", &n, &k, &t);
    scanf("%s", s + 1);
    for (int i = 1; i <= n; i++) {
        int c = s[i] - '1';
        for (int j = 0; j < 2; j++) {
            acc[j][i] = acc[j][i - 1];
        }
        if (c < 2) {
            acc[c][i]++;
        }
    }

    int nw = max(0, acc[0][n] + acc[1][n] - k); 
    int first = t + 1;
    int last = n - t;
    int res = -1;

    for (int a = first; a <= last; a++) {
        for (int b = a; b <= last; b++) {
            int wd = (acc[0][b] - acc[0][a - 1]) + (acc[1][b] - acc[1][a - 1]);
            int pw = acc[1][a - t - 1] + (acc[1][n] - acc[1][b + t]);
            int l = n - (b - a + 1) - 2 * t;
            int aw = max(0, nw - wd);
            if (aw > pw) {
                continue;
            }
            res = max(res, l - aw);
        }
    }

    int pw = acc[1][n];
    if (nw <= pw) {
        res = max(res, n - nw);
    }

    printf("%d\n", res);
}


// g++ -std=c++17 -Wall -Wextra -Wshadow B.cpp -o B